Add a cancelation checker

resolution.py

@@ -0,0 +1,32 @@
+from emis_funky_funktions import *
+
+from ir import IRNeg, IRProp, IRTerm, IRVar, Substitutions, unify, unify_clauses
+
+def terms_cancel(t1: IRTerm, t2: IRTerm) -> Option[Substitutions]:
+	"""
+	Determine if two terms could cancel each other out, given the right substitutions
+
+	That is, is there some set of substitutions such that t1 = ¬t2 or ¬t1 = t2?
+
+	If negation is possible and a substitution exists, that substitution is returned.
+	Otherwise, `None` is returned.
+
+	>>> terms_cancel(IRNeg(IRVar('x1')), IRProp('Terezi'))
+	Some((Terezi()/x1,))
+
+	>>> terms_cancel(IRProp('Nepeta'), IRVar('x1'))
+	Some((¬Nepeta()/x1,))
+
+	>>> terms_cancel(IRProp('ancestor', [IRVar('x1')]), IRVar('x1')) is None
+	True
+	"""
+	match (t1, t2):
+		case (IRNeg(a), b) | (b, IRNeg(a)): #type: ignore
+			return hush(unify(a, b))
+		case (IRVar(_) as x, a) | (a, IRVar(_) as x): #type: ignore
+			return hush(unify(x, IRNeg(a)))
+	return None
+
+if __name__ == '__main__':
+	import doctest
+	doctest.testmod()