from z3 import *
s = Solver()
bv_size = 4
a, b = BitVecs('a b', bv_size)
x    = BitVec('x', bv_size)
lhs,rhs  = BitVecs('lhs rhs', bv_size)


s.add(lhs == ((x+a)^b)-a)
s.add(rhs == ((x-a)^b)+a)
s.push()
s.add(ForAll(x, lhs == rhs))
# enumerate all possible solutions:
results=[]
while True:
  if s.check() == sat:
    m = s.model()
    print (m)
    results.append(m)
    block = []
    block = [a != m[a].as_long(), b != m[b].as_long()]
    s.add(Or(block))
  else:
    print ("results total=", len(results))
    break
#print(s.sexpr())

s.pop()
s.add(Exists(x, lhs != rhs))
result = s.check()
print(result)
if result == sat:
    print(f"Example where lhs != rhs: {s.model()}")