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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_protein_substitution_language() -> ParserElement: """Build a protein substitution parser."""

    parser_element = psub_tag + nest(
        amino_acid(PSUB_REFERENCE),
        ppc.integer(PSUB_POSITION),
        amino_acid(PSUB_VARIANT),
    )
    parser_element.setParseAction(_handle_psub)
    return parser_element