The paper describes equivalent transformations of Sisal 3.1 language structures in detail. The programming language Sisal 3.1 is based on Sisal 90. Transformations are aimed to to decomposition of complex language structures into more simple ones that can be directly expressed by an internal representation IR1 based on an intermediate form language IF1. Currently some description of similar transformations can be found in few works about Sisal 90 in the form of examples. The specified transformations are actually performed inside the front-end compiler from Sisal 3.1 into the internal representation IR1 and can be used to better understand its translation strategy. The paper also briefly (but sufficiently for understanding) describes the difference between Sisal 3.1 and Sisal 90.