I am reading the draft of a paper written by someone whose native language was not English and so who might not have been using the same abbreviations that I am familiar with, or maybe he was using standard ones and I am simply not familiar with the abbreviations involved. I can't ask him, as he is deceased. I quote: "The properties of the event plane are described by the homogeneous two-dimensional Lorentz group L: x' = xchθ + τshθ τ' = xshθ + τchθ where the hyperbolic angle θ is the transformation parameter. The relation of θ to the relativity velocity β is given by β = thθ. The coordinate τ = ct,..." What are ch, sh, and th? Did he mean cosh, sinh, and tanh? Are his abbreviations standard? Thanks.