What does kEI mean??

kei = kelvin\_kei(x) evaluates an approximation to the Kelvin function kei x. The function is based on several Chebyshev expansions. For large x, kei x is so small that it cannot be computed without underflow and the function fails.

kei (output, double)

Approximation of the Kelvin function kei x.

not only in mathematics, scientific proof also are required in the other field of science. also maths proofs are of particular structure, containing steps and logics. so proving is like doing science, it is science. that's why it is important to prove. 

an inaccurate proof leads to errors, or stating results that are not accurate.  which wil mess the probelm up you dont want this