# Guess which symbol to use for derivative, integral, etc.



guess = ->
  p = pop()
  push(p)
  if (Find(p, symbol(SYMBOL_X)))
    push_symbol(SYMBOL_X)
  else if (Find(p, symbol(SYMBOL_Y)))
    push_symbol(SYMBOL_Y)
  else if (Find(p, symbol(SYMBOL_Z)))
    push_symbol(SYMBOL_Z)
  else if (Find(p, symbol(SYMBOL_T)))
    push_symbol(SYMBOL_T)
  else if (Find(p, symbol(SYMBOL_S)))
    push_symbol(SYMBOL_S)
  else
    push_symbol(SYMBOL_X)