168: Highlights

If you want to combine two Boolean expressions, and the result is to be true if the values of both expressions are true, then send the first Boolean expression the & message with the second Boolean expression as an argument.
If you want to combine two Boolean expressions, and the result is to be true if the value of either expression is true, then send the first Boolean expression the | message with the second Boolean expression as an argument.
If you want to combine two Boolean expressions, and the result is to be true if the values of both expressions are true, and you want to prevent wasted computation, then send the first Boolean expression the and: message with the second Boolean expression embedded in a block argument.
If you want to combine two Boolean expressions, and the result is to be true if the value of either expression is true, and you want to prevent wasted computation, then send the first Boolean expression the or: message with the second Boolean expression embedded in a block argument.