ECMA Standard 367
ECMA Standard 367 -- Eiffel: Analysis, Design, and Programming Language
Standard Eiffel syntax, validity, and semantics are described in this document, which is available online.
ECMA-367 is a specification for the Eiffel programming language. Therefore, it can be useful as a reference, but it is definitely not a tutorial. That said, the document does contain occasional informative text and a general description chapter which can help readers understand the specification.