It was a proven formula, and one retailers could be comfortable with.

Critics of the changes said they amounted to tampering with a proven formula.

There are no rules, and there is no proven formula for success in this as yet.

Each side can submit its case to us, and we will use our proven formulas to find an equitable solution.

Now, Sun is shelving its proven formula in favor of a bet on continued fast growth.

As for Der Spiegel itself, changes in its proven formula are limited indeed.

On gun control, the platform repeats the proven formula for failure through stronger enforcement of existing laws.

British editors are regarded as a proven formula.

And that's a proven winning formula for a game.

The eight schools have responded because of a proven formula.