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The Catholic Church teaches that Muslims [...] adore the one and merciful God.

In the first place amongst these there are the Muslims, who, professing to hold the faith of Abraham, along with us adore the one and merciful God, who on the last day will judge mankind. - Cf. Dogmatic Constitution on the Church > Lumen gentium and CCC 841.

There are some Catholics who disagree that Muslims and Catholics "worship the same God". Thus to me disagreeing with Church teaching.

What are their arguments that Allah is not God?