lib/integral.js
function(expr, context, subIntegral) {
      if(expr.type === 'ParenthesisNode') {
        var int = subIntegral(expr.content, context, "parentheses removal");
        return int ? new ParenthesisNode(int) : null;
      }
    }
function(expr, context, subIntegral) {
      if(expr.type === 'ParenthesisNode') {
        var int = subIntegral(expr.content, context, "parentheses removal");
        return int ? new ParenthesisNode(int) : null;
      }
    }
Ignore parentheses