def texlabel(key, letter):
    """
    Args:
        key (list of string): list of parameter strings
        letter (string): planet letter

    Returns:
        string: LaTeX label for parameter string
    """
    if key.count('mpsini') == 1:
        return '$M_' + letter + '\\sin i$'
    if key.count('rhop') == 1:
        return '$\\rho_' + letter + '$'
    if key.count('a') == 1:
        return "$a_" + letter + "$"