Ad 1) Two five-star reviews on amazon UK:

https://www.amazon.co.uk/Algorithmic-Problem-Solving-Roland-...

E. Hehner has a course called "Formal Methods for Software Design", which he presents completely openly online (including video lectures, a textbook, solutions, and so on): http://www.cs.toronto.edu/~hehner/FMSD/

I really liked it.

I also liked R. Backhouse's approach to it, encapsulated in two books:

1) less playful: http://www.amazon.com/Program-Construction-Calculating-Imple...

2) more playful: http://www.amazon.com/Algorithmic-Problem-Solving-Roland-Bac...

If you are looking for motivation, you might also like: http://research.microsoft.com/en-us/um/people/lamport/pubs/p...

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I found Dijkstra's stuff to be easier to read after I had read books by Hehner/Backhouse, even though chronologically, Dijkstra came first.