Basically if you operate between any airport pair, with three individual routes who have frequencies of 1.5, 2.5, 1.5, (Or any number with a .5 after it, as denoted by "n") you are in violation of the rule. In most cases people setup one route on any airport pair and just have higher frequencies if they require them.
Just a few more examples
ABC-DEF; 1.5 2.5 0.5 - Violating Rule
ABC-DEF; 0.5 1.5 - Okay
ABC-DEF; 1, 1.5 - Okay
ABC-DEF; 1, 2, 1 - Okay
ABC-DEF; 0.5, 1, 1.5, 0.5 - Violating Rule
