SHELL_SCRIPT
  COMMANDS_LIST
    ASSIGNMENT_COMMAND
      LITERAL
        PsiElement(word)('result')
      PsiElement(=)('=')
      PsiElement($)('$')
      ARITHMETIC_EXPANSION
        PsiElement(()('(')
        PsiElement(()('(')
        LITERAL_EXPRESSION
          VARIABLE
            PsiElement(var)('$lhs')
          PsiWhiteSpace(' ')
          VARIABLE
            PsiElement(var)('$operand')
          PsiWhiteSpace(' ')
          VARIABLE
            PsiElement(var)('$rhs')
        PsiElement())(')')
        PsiElement())(')')