Выводит ошибку “Error:(105, 35) Unresolved reference: builderExpression”. Как исправить?

package com.kotlinapp.computer.cor


import android.content.ContentValues
import android.content.Context
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.widget.TextView
import android.widget.Toast
import kotlinx.coroutines.experimental.android.UI
import kotlin.coroutines.experimental.CoroutineContext
import android.os.AsyncTask
import com.kotlinapp.computer.cor.R.id.text
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.coroutines.experimental.*
import okhttp3.*
import org.w3c.dom.Text
import java.io.IOException
import kotlin.coroutines.experimental.coroutineContext
//import android.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
//import net.objecthunter.exp4j.ExpressionBuilder
import builder.Expression.*

    class MainActivity : AppCompatActivity()
    {

        override fun onCreate(savedInstanceState: Bundle?)
        {
            super.onCreate(savedInstanceState)
            setContentView(R.layout.activity_main)


            /*Number Buttons*/

            tvOne.setOnClickListener {
                evaluateExpression("1", clear = true)
            }

            tvTwo.setOnClickListener {
                evaluateExpression("2", clear = true)
            }

            tvThree.setOnClickListener {
                evaluateExpression("3", clear = true)
            }
            tvFour.setOnClickListener {
                evaluateExpression("4", clear = true)
            }

            tvFive.setOnClickListener {
                evaluateExpression("5", clear = true)
            }

            tvSix.setOnClickListener {
                evaluateExpression("6", clear = true)
            }

            tvSeven.setOnClickListener {
                evaluateExpression("7", clear = true)
            }

            tvEight.setOnClickListener {
                evaluateExpression("8", clear = true)
            }

            tvNine.setOnClickListener {
                evaluateExpression("9", clear = true)
            }

            tvZero.setOnClickListener {
                evaluateExpression("0", clear = true)
            }

            /*Operators*/

            tvPlus.setOnClickListener {
                evaluateExpression("+", clear = true)
            }

            tvMinus.setOnClickListener {
                evaluateExpression("-", clear = true)
            }

            tvMul.setOnClickListener {
                evaluateExpression("*", clear = true)
            }

            tvDivide.setOnClickListener {
                evaluateExpression("/", clear = true)
            }

            tvDot.setOnClickListener {
                evaluateExpression(".", clear = true)
            }

            tvClear.setOnClickListener {
                tvExpression.text = ""
                tvResult.text = ""
            }

            tvEquals.setOnClickListener {
                val text = tvExpression.text.toString()
                val expression = builder.Expression(text).build()

                val result = expression.evaluate()
                val longResult = result.toLong()
                if (result == longResult.toDouble()) {
                    tvResult.text = longResult.toString()
                } else {
                    tvResult.text = result.toString()
                }
            }

            tvBack.setOnClickListener {
                val text = tvExpression.text.toString()
                if(text.isNotEmpty()) {
                    tvExpression.text = text.drop(1)
                }

                tvResult.text = ""
            }
        }

        /*Function to calculate the expressions using expression builder library*/

        fun evaluateExpression(string: String, clear: Boolean) {
            if(clear) {
                tvResult.text = ""
                tvExpression.append(string)
            } else {
                tvExpression.append(tvResult.text)
                tvExpression.append(string)
                tvResult.text = ""
            }
        }