code: private static void mutateInstructionConstant(Program program, LGP manager, RandEngine randEngine)
     {
        Instruction selected_instruction = null;
        for (Instruction instruction : program.getInstructions())
        {
           if (!instruction.isStructuralIntron() && (instruction.getOperand1().isConstant() || instruction.getOperand2().isConstant()))
           {
              if (selected_instruction == null)
              {
                 selected_instruction = instruction;
              }
              else if (randEngine.uniform() < 0.5)
              {
                 selected_instruction = instruction;
              }
           }
  
        }
        if (selected_instruction != null)
        {
           InstructionHelper.mutateConstant(selected_instruction, randEngine, manager.getMicroMutateConstantStandardDeviation());
        }
     }
docs: / </summary>