diff --git a/scripts/config/expr.c b/scripts/config/expr.c
new file mode 100644
index 0000000..d1af2a5
--- /dev/null
+++ b/scripts/config/expr.c
@@ -0,0 +1,1054 @@
+/*
+ * Copyright (C) 2002 Roman Zippel <zippel@linux-m68k.org>
+ * Released under the terms of the GNU GPL v2.0.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define LKC_DIRECT_LINK
+#include "lkc.h"
+
+struct expr *expr_alloc_symbol(struct symbol *sym)
+{
+	struct expr *e = malloc(sizeof(*e));
+	memset(e, 0, sizeof(*e));
+	e->type = E_SYMBOL;
+	e->left.sym = sym;
+	return e;
+}
+
+struct expr *expr_alloc_one(enum expr_type type, struct expr *ce)
+{
+	struct expr *e = malloc(sizeof(*e));
+	memset(e, 0, sizeof(*e));
+	e->type = type;
+	e->left.expr = ce;
+	return e;
+}
+
+struct expr *expr_alloc_two(enum expr_type type, struct expr *e1, struct expr *e2)
+{
+	struct expr *e = malloc(sizeof(*e));
+	memset(e, 0, sizeof(*e));
+	e->type = type;
+	e->left.expr = e1;
+	e->right.expr = e2;
+	return e;
+}
+
+struct expr *expr_alloc_comp(enum expr_type type, struct symbol *s1, struct symbol *s2)
+{
+	struct expr *e = malloc(sizeof(*e));
+	memset(e, 0, sizeof(*e));
+	e->type = type;
+	e->left.sym = s1;
+	e->right.sym = s2;
+	return e;
+}
+
+struct expr *expr_alloc_and(struct expr *e1, struct expr *e2)
+{
+	if (!e1)
+		return e2;
+	return e2 ? expr_alloc_two(E_AND, e1, e2) : e1;
+}
+
+struct expr *expr_copy(struct expr *org)
+{
+	struct expr *e;
+
+	if (!org)
+		return NULL;
+
+	e = malloc(sizeof(*org));
+	memcpy(e, org, sizeof(*org));
+	switch (org->type) {
+	case E_SYMBOL:
+		e->left = org->left;
+		break;
+	case E_NOT:
+		e->left.expr = expr_copy(org->left.expr);
+		break;
+	case E_EQUAL:
+	case E_UNEQUAL:
+		e->left.sym = org->left.sym;
+		e->right.sym = org->right.sym;
+		break;
+	case E_AND:
+	case E_OR:
+	case E_CHOICE:
+		e->left.expr = expr_copy(org->left.expr);
+		e->right.expr = expr_copy(org->right.expr);
+		break;
+	default:
+		printf("can't copy type %d\n", e->type);
+		free(e);
+		e = NULL;
+		break;
+	}
+
+	return e;
+}
+
+void expr_free(struct expr *e)
+{
+	if (!e)
+		return;
+
+	switch (e->type) {
+	case E_SYMBOL:
+		break;
+	case E_NOT:
+		expr_free(e->left.expr);
+		return;
+	case E_EQUAL:
+	case E_UNEQUAL:
+		break;
+	case E_OR:
+	case E_AND:
+		expr_free(e->left.expr);
+		expr_free(e->right.expr);
+		break;
+	default:
+		printf("how to free type %d?\n", e->type);
+		break;
+	}
+	free(e);
+}
+
+static int trans_count;
+
+#define e1 (*ep1)
+#define e2 (*ep2)
+
+static void __expr_eliminate_eq(enum expr_type type, struct expr **ep1, struct expr **ep2)
+{
+	if (e1->type == type) {
+		__expr_eliminate_eq(type, &e1->left.expr, &e2);
+		__expr_eliminate_eq(type, &e1->right.expr, &e2);
+		return;
+	}
+	if (e2->type == type) {
+		__expr_eliminate_eq(type, &e1, &e2->left.expr);
+		__expr_eliminate_eq(type, &e1, &e2->right.expr);
+		return;
+	}
+	if (e1->type == E_SYMBOL && e2->type == E_SYMBOL &&
+	    e1->left.sym == e2->left.sym && (e1->left.sym->flags & (SYMBOL_YES|SYMBOL_NO)))
+		return;
+	if (!expr_eq(e1, e2))
+		return;
+	trans_count++;
+	expr_free(e1); expr_free(e2);
+	switch (type) {
+	case E_OR:
+		e1 = expr_alloc_symbol(&symbol_no);
+		e2 = expr_alloc_symbol(&symbol_no);
+		break;
+	case E_AND:
+		e1 = expr_alloc_symbol(&symbol_yes);
+		e2 = expr_alloc_symbol(&symbol_yes);
+		break;
+	default:
+		;
+	}
+}
+
+void expr_eliminate_eq(struct expr **ep1, struct expr **ep2)
+{
+	if (!e1 || !e2 || e1->type != e2->type)
+		return;
+	__expr_eliminate_eq(e1->type, ep1, ep2);
+	e1 = expr_eliminate_yn(e1);
+	e2 = expr_eliminate_yn(e2);
+}
+
+#undef e1
+#undef e2
+
+int expr_eq(struct expr *e1, struct expr *e2)
+{
+	int res, old_count;
+
+	if (e1->type != e2->type)
+		return 0;
+	switch (e1->type) {
+	case E_EQUAL:
+	case E_UNEQUAL:
+		return e1->left.sym == e2->left.sym && e1->right.sym == e2->right.sym;
+	case E_SYMBOL:
+		return e1->left.sym == e2->left.sym;
+	case E_NOT:
+		return expr_eq(e1->left.expr, e2->left.expr);
+	case E_AND:
+	case E_OR:
+		e1 = expr_copy(e1);
+		e2 = expr_copy(e2);
+		old_count = trans_count;
+		expr_eliminate_eq(&e1, &e2);
+		res = (e1->type == E_SYMBOL && e2->type == E_SYMBOL &&
+		       e1->left.sym == e2->left.sym);
+		expr_free(e1);
+		expr_free(e2);
+		trans_count = old_count;
+		return res;
+	case E_CHOICE:
+	case E_NONE:
+		/* panic */;
+	}
+
+	print_expr(0, e1, 0);
+	printf(" = ");
+	print_expr(0, e2, 0);
+	printf(" ?\n");
+
+	return 0;
+}
+
+struct expr *expr_eliminate_yn(struct expr *e)
+{
+	struct expr *tmp;
+
+	if (e) switch (e->type) {
+	case E_AND:
+		e->left.expr = expr_eliminate_yn(e->left.expr);
+		e->right.expr = expr_eliminate_yn(e->right.expr);
+		if (e->left.expr->type == E_SYMBOL) {
+			if (e->left.expr->left.sym == &symbol_no) {
+				expr_free(e->left.expr);
+				expr_free(e->right.expr);
+				e->type = E_SYMBOL;
+				e->left.sym = &symbol_no;
+				e->right.expr = NULL;
+				return e;
+			} else if (e->left.expr->left.sym == &symbol_yes) {
+				free(e->left.expr);
+				tmp = e->right.expr;
+				*e = *(e->right.expr);
+				free(tmp);
+				return e;
+			}
+		}
+		if (e->right.expr->type == E_SYMBOL) {
+			if (e->right.expr->left.sym == &symbol_no) {
+				expr_free(e->left.expr);
+				expr_free(e->right.expr);
+				e->type = E_SYMBOL;
+				e->left.sym = &symbol_no;
+				e->right.expr = NULL;
+				return e;
+			} else if (e->right.expr->left.sym == &symbol_yes) {
+				free(e->right.expr);
+				tmp = e->left.expr;
+				*e = *(e->left.expr);
+				free(tmp);
+				return e;
+			}
+		}
+		break;
+	case E_OR:
+		e->left.expr = expr_eliminate_yn(e->left.expr);
+		e->right.expr = expr_eliminate_yn(e->right.expr);
+		if (e->left.expr->type == E_SYMBOL) {
+			if (e->left.expr->left.sym == &symbol_no) {
+				free(e->left.expr);
+				tmp = e->right.expr;
+				*e = *(e->right.expr);
+				free(tmp);
+				return e;
+			} else if (e->left.expr->left.sym == &symbol_yes) {
+				expr_free(e->left.expr);
+				expr_free(e->right.expr);
+				e->type = E_SYMBOL;
+				e->left.sym = &symbol_yes;
+				e->right.expr = NULL;
+				return e;
+			}
+		}
+		if (e->right.expr->type == E_SYMBOL) {
+			if (e->right.expr->left.sym == &symbol_no) {
+				free(e->right.expr);
+				tmp = e->left.expr;
+				*e = *(e->left.expr);
+				free(tmp);
+				return e;
+			} else if (e->right.expr->left.sym == &symbol_yes) {
+				expr_free(e->left.expr);
+				expr_free(e->right.expr);
+				e->type = E_SYMBOL;
+				e->left.sym = &symbol_yes;
+				e->right.expr = NULL;
+				return e;
+			}
+		}
+		break;
+	default:
+		;
+	}
+	return e;
+}
+
+/*
+ * bool FOO!=n => FOO
+ */
+struct expr *expr_trans_bool(struct expr *e)
+{
+	if (!e)
+		return NULL;
+	switch (e->type) {
+	case E_AND:
+	case E_OR:
+	case E_NOT:
+		e->left.expr = expr_trans_bool(e->left.expr);
+		e->right.expr = expr_trans_bool(e->right.expr);
+		break;
+	case E_UNEQUAL:
+		// FOO!=n -> FOO
+		if (e->left.sym->type == S_TRISTATE) {
+			if (e->right.sym == &symbol_no) {
+				e->type = E_SYMBOL;
+				e->right.sym = NULL;
+			}
+		}
+		break;
+	default:
+		;
+	}
+	return e;
+}
+
+/*
+ * e1 || e2 -> ?
+ */
+struct expr *expr_join_or(struct expr *e1, struct expr *e2)
+{
+	struct expr *tmp;
+	struct symbol *sym1, *sym2;
+
+	if (expr_eq(e1, e2))
+		return expr_copy(e1);
+	if (e1->type != E_EQUAL && e1->type != E_UNEQUAL && e1->type != E_SYMBOL && e1->type != E_NOT)
+		return NULL;
+	if (e2->type != E_EQUAL && e2->type != E_UNEQUAL && e2->type != E_SYMBOL && e2->type != E_NOT)
+		return NULL;
+	if (e1->type == E_NOT) {
+		tmp = e1->left.expr;
+		if (tmp->type != E_EQUAL && tmp->type != E_UNEQUAL && tmp->type != E_SYMBOL)
+			return NULL;
+		sym1 = tmp->left.sym;
+	} else
+		sym1 = e1->left.sym;
+	if (e2->type == E_NOT) {
+		if (e2->left.expr->type != E_SYMBOL)
+			return NULL;
+		sym2 = e2->left.expr->left.sym;
+	} else
+		sym2 = e2->left.sym;
+	if (sym1 != sym2)
+		return NULL;
+	if (sym1->type != S_BOOLEAN && sym1->type != S_TRISTATE)
+		return NULL;
+	if (sym1->type == S_TRISTATE) {
+		if (e1->type == E_EQUAL && e2->type == E_EQUAL &&
+		    ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_mod) ||
+		     (e1->right.sym == &symbol_mod && e2->right.sym == &symbol_yes))) {
+			// (a='y') || (a='m') -> (a!='n')
+			return expr_alloc_comp(E_UNEQUAL, sym1, &symbol_no);
+		}
+		if (e1->type == E_EQUAL && e2->type == E_EQUAL &&
+		    ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_no) ||
+		     (e1->right.sym == &symbol_no && e2->right.sym == &symbol_yes))) {
+			// (a='y') || (a='n') -> (a!='m')
+			return expr_alloc_comp(E_UNEQUAL, sym1, &symbol_mod);
+		}
+		if (e1->type == E_EQUAL && e2->type == E_EQUAL &&
+		    ((e1->right.sym == &symbol_mod && e2->right.sym == &symbol_no) ||
+		     (e1->right.sym == &symbol_no && e2->right.sym == &symbol_mod))) {
+			// (a='m') || (a='n') -> (a!='y')
+			return expr_alloc_comp(E_UNEQUAL, sym1, &symbol_yes);
+		}
+	}
+	if (sym1->type == S_BOOLEAN && sym1 == sym2) {
+		if ((e1->type == E_NOT && e1->left.expr->type == E_SYMBOL && e2->type == E_SYMBOL) ||
+		    (e2->type == E_NOT && e2->left.expr->type == E_SYMBOL && e1->type == E_SYMBOL))
+			return expr_alloc_symbol(&symbol_yes);
+	}
+
+	printf("optimize ");
+	print_expr(0, e1, 0);
+	printf(" || ");
+	print_expr(0, e2, 0);
+	printf(" ?\n");
+	return NULL;
+}
+
+struct expr *expr_join_and(struct expr *e1, struct expr *e2)
+{
+	struct expr *tmp;
+	struct symbol *sym1, *sym2;
+
+	if (expr_eq(e1, e2))
+		return expr_copy(e1);
+	if (e1->type != E_EQUAL && e1->type != E_UNEQUAL && e1->type != E_SYMBOL && e1->type != E_NOT)
+		return NULL;
+	if (e2->type != E_EQUAL && e2->type != E_UNEQUAL && e2->type != E_SYMBOL && e2->type != E_NOT)
+		return NULL;
+	if (e1->type == E_NOT) {
+		tmp = e1->left.expr;
+		if (tmp->type != E_EQUAL && tmp->type != E_UNEQUAL && tmp->type != E_SYMBOL)
+			return NULL;
+		sym1 = tmp->left.sym;
+	} else
+		sym1 = e1->left.sym;
+	if (e2->type == E_NOT) {
+		if (e2->left.expr->type != E_SYMBOL)
+			return NULL;
+		sym2 = e2->left.expr->left.sym;
+	} else
+		sym2 = e2->left.sym;
+	if (sym1 != sym2)
+		return NULL;
+	if (sym1->type != S_BOOLEAN && sym1->type != S_TRISTATE)
+		return NULL;
+
+	if ((e1->type == E_SYMBOL && e2->type == E_EQUAL && e2->right.sym == &symbol_yes) ||
+	    (e2->type == E_SYMBOL && e1->type == E_EQUAL && e1->right.sym == &symbol_yes))
+		// (a) && (a='y') -> (a='y')
+		return expr_alloc_comp(E_EQUAL, sym1, &symbol_yes);
+
+	if ((e1->type == E_SYMBOL && e2->type == E_UNEQUAL && e2->right.sym == &symbol_no) ||
+	    (e2->type == E_SYMBOL && e1->type == E_UNEQUAL && e1->right.sym == &symbol_no))
+		// (a) && (a!='n') -> (a)
+		return expr_alloc_symbol(sym1);
+
+	if (sym1->type == S_TRISTATE) {
+		if (e1->type == E_EQUAL && e2->type == E_UNEQUAL) {
+			// (a='b') && (a!='c') -> 'b'='c' ? 'n' : a='b'
+			sym2 = e1->right.sym;
+			if ((e2->right.sym->flags & SYMBOL_CONST) && (sym2->flags & SYMBOL_CONST))
+				return sym2 != e2->right.sym ? expr_alloc_comp(E_EQUAL, sym1, sym2)
+							     : expr_alloc_symbol(&symbol_no);
+		}
+		if (e1->type == E_UNEQUAL && e2->type == E_EQUAL) {
+			// (a='b') && (a!='c') -> 'b'='c' ? 'n' : a='b'
+			sym2 = e2->right.sym;
+			if ((e1->right.sym->flags & SYMBOL_CONST) && (sym2->flags & SYMBOL_CONST))
+				return sym2 != e1->right.sym ? expr_alloc_comp(E_EQUAL, sym1, sym2)
+							     : expr_alloc_symbol(&symbol_no);
+		}
+		if (e1->type == E_UNEQUAL && e2->type == E_UNEQUAL &&
+			   ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_no) ||
+			    (e1->right.sym == &symbol_no && e2->right.sym == &symbol_yes)))
+			// (a!='y') && (a!='n') -> (a='m')
+			return expr_alloc_comp(E_EQUAL, sym1, &symbol_mod);
+
+		if (e1->type == E_UNEQUAL && e2->type == E_UNEQUAL &&
+			   ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_mod) ||
+			    (e1->right.sym == &symbol_mod && e2->right.sym == &symbol_yes)))
+			// (a!='y') && (a!='m') -> (a='n')
+			return expr_alloc_comp(E_EQUAL, sym1, &symbol_no);
+
+		if (e1->type == E_UNEQUAL && e2->type == E_UNEQUAL &&
+			   ((e1->right.sym == &symbol_mod && e2->right.sym == &symbol_no) ||
+			    (e1->right.sym == &symbol_no && e2->right.sym == &symbol_mod)))
+			// (a!='m') && (a!='n') -> (a='m')
+			return expr_alloc_comp(E_EQUAL, sym1, &symbol_yes);
+
+		if ((e1->type == E_SYMBOL && e2->type == E_EQUAL && e2->right.sym == &symbol_mod) ||
+		    (e2->type == E_SYMBOL && e1->type == E_EQUAL && e1->right.sym == &symbol_mod) ||
+		    (e1->type == E_SYMBOL && e2->type == E_UNEQUAL && e2->right.sym == &symbol_yes) ||
+		    (e2->type == E_SYMBOL && e1->type == E_UNEQUAL && e1->right.sym == &symbol_yes))
+			return NULL;
+	}
+	printf("optimize ");
+	print_expr(0, e1, 0);
+	printf(" && ");
+	print_expr(0, e2, 0);
+	printf(" ?\n");
+	return NULL;
+}
+
+static void expr_eliminate_dups1(enum expr_type type, struct expr **ep1, struct expr **ep2)
+{
+#define e1 (*ep1)
+#define e2 (*ep2)
+	struct expr *tmp;
+
+	if (e1->type == type) {
+		expr_eliminate_dups1(type, &e1->left.expr, &e2);
+		expr_eliminate_dups1(type, &e1->right.expr, &e2);
+		return;
+	}
+	if (e2->type == type) {
+		expr_eliminate_dups1(type, &e1, &e2->left.expr);
+		expr_eliminate_dups1(type, &e1, &e2->right.expr);
+		return;
+	}
+	if (e1 == e2)
+		return;
+
+	switch (e1->type) {
+	case E_OR: case E_AND:
+		expr_eliminate_dups1(e1->type, &e1, &e1);
+	default:
+		;
+	}
+
+	switch (type) {
+	case E_OR:
+		tmp = expr_join_or(e1, e2);
+		if (tmp) {
+			expr_free(e1); expr_free(e2);
+			e1 = expr_alloc_symbol(&symbol_no);
+			e2 = tmp;
+			trans_count++;
+		}
+		break;
+	case E_AND:
+		tmp = expr_join_and(e1, e2);
+		if (tmp) {
+			expr_free(e1); expr_free(e2);
+			e1 = expr_alloc_symbol(&symbol_yes);
+			e2 = tmp;
+			trans_count++;
+		}
+		break;
+	default:
+		;
+	}
+#undef e1
+#undef e2
+}
+
+static void expr_eliminate_dups2(enum expr_type type, struct expr **ep1, struct expr **ep2)
+{
+#define e1 (*ep1)
+#define e2 (*ep2)
+	struct expr *tmp, *tmp1, *tmp2;
+
+	if (e1->type == type) {
+		expr_eliminate_dups2(type, &e1->left.expr, &e2);
+		expr_eliminate_dups2(type, &e1->right.expr, &e2);
+		return;
+	}
+	if (e2->type == type) {
+		expr_eliminate_dups2(type, &e1, &e2->left.expr);
+		expr_eliminate_dups2(type, &e1, &e2->right.expr);
+	}
+	if (e1 == e2)
+		return;
+
+	switch (e1->type) {
+	case E_OR:
+		expr_eliminate_dups2(e1->type, &e1, &e1);
+		// (FOO || BAR) && (!FOO && !BAR) -> n
+		tmp1 = expr_transform(expr_alloc_one(E_NOT, expr_copy(e1)));
+		tmp2 = expr_copy(e2);
+		tmp = expr_extract_eq_and(&tmp1, &tmp2);
+		if (expr_is_yes(tmp1)) {
+			expr_free(e1);
+			e1 = expr_alloc_symbol(&symbol_no);
+			trans_count++;
+		}
+		expr_free(tmp2);
+		expr_free(tmp1);
+		expr_free(tmp);
+		break;
+	case E_AND:
+		expr_eliminate_dups2(e1->type, &e1, &e1);
+		// (FOO && BAR) || (!FOO || !BAR) -> y
+		tmp1 = expr_transform(expr_alloc_one(E_NOT, expr_copy(e1)));
+		tmp2 = expr_copy(e2);
+		tmp = expr_extract_eq_or(&tmp1, &tmp2);
+		if (expr_is_no(tmp1)) {
+			expr_free(e1);
+			e1 = expr_alloc_symbol(&symbol_yes);
+			trans_count++;
+		}
+		expr_free(tmp2);
+		expr_free(tmp1);
+		expr_free(tmp);
+		break;
+	default:
+		;
+	}
+#undef e1
+#undef e2
+}
+
+struct expr *expr_eliminate_dups(struct expr *e)
+{
+	int oldcount;
+	if (!e)
+		return e;
+
+	oldcount = trans_count;
+	while (1) {
+		trans_count = 0;
+		switch (e->type) {
+		case E_OR: case E_AND:
+			expr_eliminate_dups1(e->type, &e, &e);
+			expr_eliminate_dups2(e->type, &e, &e);
+		default:
+			;
+		}
+		if (!trans_count)
+			break;
+		e = expr_eliminate_yn(e);
+	}
+	trans_count = oldcount;
+	return e;
+}
+
+struct expr *expr_transform(struct expr *e)
+{
+	struct expr *tmp;
+
+	if (!e)
+		return NULL;
+	switch (e->type) {
+	case E_EQUAL:
+	case E_UNEQUAL:
+	case E_SYMBOL:
+	case E_CHOICE:
+		break;
+	default:
+		e->left.expr = expr_transform(e->left.expr);
+		e->right.expr = expr_transform(e->right.expr);
+	}
+
+	switch (e->type) {
+	case E_EQUAL:
+		if (e->left.sym->type != S_BOOLEAN)
+			break;
+		if (e->right.sym == &symbol_no) {
+			e->type = E_NOT;
+			e->left.expr = expr_alloc_symbol(e->left.sym);
+			e->right.sym = NULL;
+			break;
+		}
+		if (e->right.sym == &symbol_mod) {
+			printf("boolean symbol %s tested for 'm'? test forced to 'n'\n", e->left.sym->name);
+			e->type = E_SYMBOL;
+			e->left.sym = &symbol_no;
+			e->right.sym = NULL;
+			break;
+		}
+		if (e->right.sym == &symbol_yes) {
+			e->type = E_SYMBOL;
+			e->right.sym = NULL;
+			break;
+		}
+		break;
+	case E_UNEQUAL:
+		if (e->left.sym->type != S_BOOLEAN)
+			break;
+		if (e->right.sym == &symbol_no) {
+			e->type = E_SYMBOL;
+			e->right.sym = NULL;
+			break;
+		}
+		if (e->right.sym == &symbol_mod) {
+			printf("boolean symbol %s tested for 'm'? test forced to 'y'\n", e->left.sym->name);
+			e->type = E_SYMBOL;
+			e->left.sym = &symbol_yes;
+			e->right.sym = NULL;
+			break;
+		}
+		if (e->right.sym == &symbol_yes) {
+			e->type = E_NOT;
+			e->left.expr = expr_alloc_symbol(e->left.sym);
+			e->right.sym = NULL;
+			break;
+		}
+		break;
+	case E_NOT:
+		switch (e->left.expr->type) {
+		case E_NOT:
+			// !!a -> a
+			tmp = e->left.expr->left.expr;
+			free(e->left.expr);
+			free(e);
+			e = tmp;
+			e = expr_transform(e);
+			break;
+		case E_EQUAL:
+		case E_UNEQUAL:
+			// !a='x' -> a!='x'
+			tmp = e->left.expr;
+			free(e);
+			e = tmp;
+			e->type = e->type == E_EQUAL ? E_UNEQUAL : E_EQUAL;
+			break;
+		case E_OR:
+			// !(a || b) -> !a && !b
+			tmp = e->left.expr;
+			e->type = E_AND;
+			e->right.expr = expr_alloc_one(E_NOT, tmp->right.expr);
+			tmp->type = E_NOT;
+			tmp->right.expr = NULL;
+			e = expr_transform(e);
+			break;
+		case E_AND:
+			// !(a && b) -> !a || !b
+			tmp = e->left.expr;
+			e->type = E_OR;
+			e->right.expr = expr_alloc_one(E_NOT, tmp->right.expr);
+			tmp->type = E_NOT;
+			tmp->right.expr = NULL;
+			e = expr_transform(e);
+			break;
+		case E_SYMBOL:
+			if (e->left.expr->left.sym == &symbol_yes) {
+				// !'y' -> 'n'
+				tmp = e->left.expr;
+				free(e);
+				e = tmp;
+				e->type = E_SYMBOL;
+				e->left.sym = &symbol_no;
+				break;
+			}
+			if (e->left.expr->left.sym == &symbol_mod) {
+				// !'m' -> 'm'
+				tmp = e->left.expr;
+				free(e);
+				e = tmp;
+				e->type = E_SYMBOL;
+				e->left.sym = &symbol_mod;
+				break;
+			}
+			if (e->left.expr->left.sym == &symbol_no) {
+				// !'n' -> 'y'
+				tmp = e->left.expr;
+				free(e);
+				e = tmp;
+				e->type = E_SYMBOL;
+				e->left.sym = &symbol_yes;
+				break;
+			}
+			break;
+		default:
+			;
+		}
+		break;
+	default:
+		;
+	}
+	return e;
+}
+
+int expr_contains_symbol(struct expr *dep, struct symbol *sym)
+{
+	if (!dep)
+		return 0;
+
+	switch (dep->type) {
+	case E_AND:
+	case E_OR:
+		return expr_contains_symbol(dep->left.expr, sym) ||
+		       expr_contains_symbol(dep->right.expr, sym);
+	case E_SYMBOL:
+		return dep->left.sym == sym;
+	case E_EQUAL:
+	case E_UNEQUAL:
+		return dep->left.sym == sym ||
+		       dep->right.sym == sym;
+	case E_NOT:
+		return expr_contains_symbol(dep->left.expr, sym);
+	default:
+		;
+	}
+	return 0;
+}
+
+bool expr_depends_symbol(struct expr *dep, struct symbol *sym)
+{
+	if (!dep)
+		return false;
+
+	switch (dep->type) {
+	case E_AND:
+		return expr_depends_symbol(dep->left.expr, sym) ||
+		       expr_depends_symbol(dep->right.expr, sym);
+	case E_SYMBOL:
+		return dep->left.sym == sym;
+	case E_EQUAL:
+		if (dep->left.sym == sym) {
+			if (dep->right.sym == &symbol_yes || dep->right.sym == &symbol_mod)
+				return true;
+		}
+		break;
+	case E_UNEQUAL:
+		if (dep->left.sym == sym) {
+			if (dep->right.sym == &symbol_no)
+				return true;
+		}
+		break;
+	default:
+		;
+	}
+ 	return false;
+}
+
+struct expr *expr_extract_eq_and(struct expr **ep1, struct expr **ep2)
+{
+	struct expr *tmp = NULL;
+	expr_extract_eq(E_AND, &tmp, ep1, ep2);
+	if (tmp) {
+		*ep1 = expr_eliminate_yn(*ep1);
+		*ep2 = expr_eliminate_yn(*ep2);
+	}
+	return tmp;
+}
+
+struct expr *expr_extract_eq_or(struct expr **ep1, struct expr **ep2)
+{
+	struct expr *tmp = NULL;
+	expr_extract_eq(E_OR, &tmp, ep1, ep2);
+	if (tmp) {
+		*ep1 = expr_eliminate_yn(*ep1);
+		*ep2 = expr_eliminate_yn(*ep2);
+	}
+	return tmp;
+}
+
+void expr_extract_eq(enum expr_type type, struct expr **ep, struct expr **ep1, struct expr **ep2)
+{
+#define e1 (*ep1)
+#define e2 (*ep2)
+	if (e1->type == type) {
+		expr_extract_eq(type, ep, &e1->left.expr, &e2);
+		expr_extract_eq(type, ep, &e1->right.expr, &e2);
+		return;
+	}
+	if (e2->type == type) {
+		expr_extract_eq(type, ep, ep1, &e2->left.expr);
+		expr_extract_eq(type, ep, ep1, &e2->right.expr);
+		return;
+	}
+	if (expr_eq(e1, e2)) {
+		*ep = *ep ? expr_alloc_two(type, *ep, e1) : e1;
+		expr_free(e2);
+		if (type == E_AND) {
+			e1 = expr_alloc_symbol(&symbol_yes);
+			e2 = expr_alloc_symbol(&symbol_yes);
+		} else if (type == E_OR) {
+			e1 = expr_alloc_symbol(&symbol_no);
+			e2 = expr_alloc_symbol(&symbol_no);
+		}
+	}
+#undef e1
+#undef e2
+}
+
+struct expr *expr_trans_compare(struct expr *e, enum expr_type type, struct symbol *sym)
+{
+	struct expr *e1, *e2;
+
+	if (!e) {
+		e = expr_alloc_symbol(sym);
+		if (type == E_UNEQUAL)
+			e = expr_alloc_one(E_NOT, e);
+		return e;
+	}
+	switch (e->type) {
+	case E_AND:
+		e1 = expr_trans_compare(e->left.expr, E_EQUAL, sym);
+		e2 = expr_trans_compare(e->right.expr, E_EQUAL, sym);
+		if (sym == &symbol_yes)
+			e = expr_alloc_two(E_AND, e1, e2);
+		if (sym == &symbol_no)
+			e = expr_alloc_two(E_OR, e1, e2);
+		if (type == E_UNEQUAL)
+			e = expr_alloc_one(E_NOT, e);
+		return e;
+	case E_OR:
+		e1 = expr_trans_compare(e->left.expr, E_EQUAL, sym);
+		e2 = expr_trans_compare(e->right.expr, E_EQUAL, sym);
+		if (sym == &symbol_yes)
+			e = expr_alloc_two(E_OR, e1, e2);
+		if (sym == &symbol_no)
+			e = expr_alloc_two(E_AND, e1, e2);
+		if (type == E_UNEQUAL)
+			e = expr_alloc_one(E_NOT, e);
+		return e;
+	case E_NOT:
+		return expr_trans_compare(e->left.expr, type == E_EQUAL ? E_UNEQUAL : E_EQUAL, sym);
+	case E_UNEQUAL:
+	case E_EQUAL:
+		if (type == E_EQUAL) {
+			if (sym == &symbol_yes)
+				return expr_copy(e);
+			if (sym == &symbol_mod)
+				return expr_alloc_symbol(&symbol_no);
+			if (sym == &symbol_no)
+				return expr_alloc_one(E_NOT, expr_copy(e));
+		} else {
+			if (sym == &symbol_yes)
+				return expr_alloc_one(E_NOT, expr_copy(e));
+			if (sym == &symbol_mod)
+				return expr_alloc_symbol(&symbol_yes);
+			if (sym == &symbol_no)
+				return expr_copy(e);
+		}
+		break;
+	case E_SYMBOL:
+		return expr_alloc_comp(type, e->left.sym, sym);
+	case E_CHOICE:
+	case E_NONE:
+		/* panic */;
+	}
+	return NULL;
+}
+
+tristate expr_calc_value(struct expr *e)
+{
+	tristate val1, val2;
+	const char *str1, *str2;
+
+	if (!e)
+		return yes;
+
+	switch (e->type) {
+	case E_SYMBOL:
+		sym_calc_value(e->left.sym);
+		return S_TRI(e->left.sym->curr);
+	case E_AND:
+		val1 = expr_calc_value(e->left.expr);
+		val2 = expr_calc_value(e->right.expr);
+		return E_AND(val1, val2);
+	case E_OR:
+		val1 = expr_calc_value(e->left.expr);
+		val2 = expr_calc_value(e->right.expr);
+		return E_OR(val1, val2);
+	case E_NOT:
+		val1 = expr_calc_value(e->left.expr);
+		return E_NOT(val1);
+	case E_EQUAL:
+		sym_calc_value(e->left.sym);
+		sym_calc_value(e->right.sym);
+		str1 = sym_get_string_value(e->left.sym);
+		str2 = sym_get_string_value(e->right.sym);
+		return !strcmp(str1, str2) ? yes : no;
+	case E_UNEQUAL:
+		sym_calc_value(e->left.sym);
+		sym_calc_value(e->right.sym);
+		str1 = sym_get_string_value(e->left.sym);
+		str2 = sym_get_string_value(e->right.sym);
+		return !strcmp(str1, str2) ? no : yes;
+	default:
+		printf("expr_calc_value: %d?\n", e->type);
+		return no;
+	}
+}
+
+int expr_compare_type(enum expr_type t1, enum expr_type t2)
+{
+#if 0
+	return 1;
+#else
+	if (t1 == t2)
+		return 0;
+	switch (t1) {
+	case E_EQUAL:
+	case E_UNEQUAL:
+		if (t2 == E_NOT)
+			return 1;
+	case E_NOT:
+		if (t2 == E_AND)
+			return 1;
+	case E_AND:
+		if (t2 == E_OR)
+			return 1;
+	case E_OR:
+		if (t2 == E_CHOICE)
+			return 1;
+	case E_CHOICE:
+		if (t2 == 0)
+			return 1;
+	default:
+		return -1;
+	}
+	printf("[%dgt%d?]", t1, t2);
+	return 0;
+#endif
+}
+
+void expr_print(struct expr *e, void (*fn)(void *, const char *), void *data, int prevtoken)
+{
+	if (!e) {
+		fn(data, "y");
+		return;
+	}
+
+	if (expr_compare_type(prevtoken, e->type) > 0)
+		fn(data, "(");
+	switch (e->type) {
+	case E_SYMBOL:
+		if (e->left.sym->name)
+			fn(data, e->left.sym->name);
+		else
+			fn(data, "<choice>");
+		break;
+	case E_NOT:
+		fn(data, "!");
+		expr_print(e->left.expr, fn, data, E_NOT);
+		break;
+	case E_EQUAL:
+		fn(data, e->left.sym->name);
+		fn(data, "=");
+		fn(data, e->right.sym->name);
+		break;
+	case E_UNEQUAL:
+		fn(data, e->left.sym->name);
+		fn(data, "!=");
+		fn(data, e->right.sym->name);
+		break;
+	case E_OR:
+		expr_print(e->left.expr, fn, data, E_OR);
+		fn(data, " || ");
+		expr_print(e->right.expr, fn, data, E_OR);
+		break;
+	case E_AND:
+		expr_print(e->left.expr, fn, data, E_AND);
+		fn(data, " && ");
+		expr_print(e->right.expr, fn, data, E_AND);
+		break;
+	case E_CHOICE:
+		if (e->left.expr) {
+			expr_print(e->left.expr, fn, data, E_CHOICE);
+			fn(data, " ^ ");
+		}
+		fn(data, e->right.sym->name);
+		break;
+	default:
+	  {
+		char buf[32];
+		sprintf(buf, "<unknown type %d>", e->type);
+		fn(data, buf);
+		break;
+	  }
+	}
+	if (expr_compare_type(prevtoken, e->type) > 0)
+		fn(data, ")");
+}
+
+static void expr_print_file_helper(void *data, const char *str)
+{
+	fwrite(str, strlen(str), 1, data);
+}
+
+void expr_fprint(struct expr *e, FILE *out)
+{
+	expr_print(e, expr_print_file_helper, out, E_NONE);
+}
+
+void print_expr(int mask, struct expr *e, int prevtoken)
+{
+	if (!(cdebug & mask))
+		return;
+	expr_fprint(e, stdout);
+}
+