code: function(e) {
              var status = false, g = e.group;
              if(g === PL || g === CP) {
                  status = true;
                  for(var s in e.symbols) {
                      var symbol = e.symbols[s], sg = symbol.group;
                      if(sg === FN || sg === EX || sg === CB) { status = false;}
                      else {
                          if(sg === PL || sg === CP) status = __.isLinear(symbol);
                          else {
                              if(symbol.group !== N && symbol.power.toString() !== '1') { status = false; break; }
                          }
                      }
                  }
              }
              else if(g === S && e.power === 1) status = true;
              return status;
          }
docs: /*
  Checks to see if the "equation" is linear
  @param {Symbol} e
  @returns {boolean}