Theorems for judging the congruence of two triangles are all expressed in letters. * * * There are four kinds: SAS, ASA, AAS, SSS, etc. In addition to these four methods, there is a special method to judge the congruence of two right-angled triangles, that is, if a hypotenuse and a right-angled side of two right-angled triangles are equal, then the two right-angled triangles are congruent. Short for "hypotenuse and right-angled side are equal", that is, "HL" (where H stands for hypotenuse and L stands for right-angled side).

Theorems are expressed in letters only for the convenience of writing. You can also use words instead of letters to express this theorem. It is both a concrete figure and a general method, so there is no need to draw a figure.