pattern depth(primary : Primary, depth) = {
	Literal(primary);
	depth == 1;
	// Always a leaf element
} or {
	BinaryExpression(primary);
	BinaryExpression.left(primary, left);
	BinaryExpression.right(primary, right);
	
	find primaryExpressionDepth(left, ldepth);
	find primaryExpressionDepth(right, rdepth);
	
//	check(depth == Math::max(ldepth, rdepth) + 1); // No positive inference
//	depth == Math::max(ldepth, rdepth) + 1; // Invalid syntax
}