added implication elim rule

1 files changed, 18 insertions, 0 deletions

diff --git a/src/eval.c b/src/eval.c
index 4e978b6..263e1c1 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -61,6 +61,24 @@ char just_is_sound(line_t line, lineSet_t lines) {
 				return 0;
 			}
 			return peq(prop, *w.propA) || peq(prop, *w.propB);
+		case IMPLICATION_ELIM:
+			wl = lines.lines[just.references[0] - 1];
+			xl = lines.lines[just.references[1] - 1];
+			w = wl.proposition;
+			x = xl.proposition;
+			if (!seqlt(line.scope, wl.scope) || !seqlt(line.scope, xl.scope)) {
+				return 0;
+			}
+			/* find the positions of the arguments */
+			if (!w.isSimple && peq(prop, *w.propB) && w.relation == IMPLICATION && peq(x, *w.propA)) {
+				return 1;
+			}
+			else if (!x.isSimple && peq(prop, *x.propB) && x.relation == IMPLICATION && peq(w, *x.propA)) {
+				return 1;
+			}
+			else {
+				return 0;
+			}
 		default:
 			return 0;
 	}