SHELL_SCRIPT
  COMMANDS_LIST
    SIMPLE_COMMAND
      ASSIGNMENT_COMMAND
        LITERAL
          PsiElement(word)('a')
        PsiElement(=)('=')
        NUMBER
          PsiElement(int)('1')
      PsiWhiteSpace(' ')
      SIMPLE_COMMAND_ELEMENT
        ARITHMETIC_EXPANSION
          PsiElement(()('(')
          PsiElement(()('(')
          LITERAL_EXPRESSION
            NUMBER
              PsiElement(int)('1')
          PsiElement())(')')
          PsiElement())(')')