Welsh Rules: The Welsh Grammar for Learners by Heini Gruffudd
This second edition Welsh grammar book is suitable for learners at all levels, both for revision and as a reference book. Presented in an entertaining style, with a great deal of humour, both in the text and in the cartoon illustrations, with English explanations, and useful grammar exercises using everyday situations such as housework, travelling, using the Internet and many others.
There are also sections on the Welsh alphabet, Welsh idioms, and an English-Welsh glossary of terms relevant to grammar.
A great volume to have for experienced learners to help with those little mistakes that won't go away!