if( debug ) Gpr.debug("Tree: " + tree.toStringTree());
Value a1 = new Value(tree.getChild(0), this);
Value c1 = new Value(tree.getChild(1), this);
Value a2 = new Value(tree.getChild(2), this);
Value c2 = new Value(tree.getChild(3), this);
MembershipFunction membershipFunction = new MembershipFunctionDifferenceSigmoidal(a1, c1, a2, c2);
return membershipFunction;
}