A popular ditty of the late nineteenth- and early twentieth-century railroad era was the following (sung to the tune of Humoresque by the nineteenth-century Czech composer Antonin Dvorak):

Passengers will please refrain – From flushing toilets – While the train – Is standing in the station – I love you.

For the preceding ditty, define a variable S expressing whether or not the train is in the station, a variable M expressing whether or not the train is moving (“standing” means “not moving”), and a variable F expressing the fact that the toilet may be flushed.