if one's memory is not at fault

If my memory is not at fault, there were 48 desks in each classroom, and every seat was occupied - a large class, it's clear now, for a single teacher.

Going down Picadilly one day and nearing Grosvenor Place I saw, if my memory is not at fault, some workmen with their coats off - or so they seemed.

'But, if my memory is not at fault, in the case of a recent murder, the doctor first gave a verdict of heart failure - altering it when the local constable pointed out that there was a bullet wound through the head!'