code: def free_symbols(self):
          
          try:
              lhs_syms = self.lhs.free_symbols
          except AttributeError:
              lhs_syms = set()
          try:
              rhs_syms = self.rhs.free_symbols
          except AttributeError:
              rhs_syms = set()
          return lhs_syms | rhs_syms
docs: Set of free SymPy symbols contained within the equation.