SmtEngine smt = new SmtEngine(em);
Type t = em.booleanType();
Expr a = em.mkVar("a", em.booleanType());
Expr b = em.mkVar("b", em.booleanType());
Expr e = new Expr(em.mkExpr(Kind.AND, a, b, new Expr(a).notExpr()));
System.out.println("==> " + e);
Result r = smt.checkSat(e);
boolean correct = r.isSat() == Result.Sat.UNSAT;