Let's say I have $easter = 0415. ( equivalent to date("md") for April 15th)

There are christian celebrations that take place some specific number of days beofre & after Easter. Now how di I deduce, for example, the date() of Mardi-Gras ? (here it happens 47 days before Easter).

Is there a way to make date on "md"-47 ? So that it would be 0228 in this case. (if I'm not mistaken)