Introductory material to logic

Someone needed this, so I made a quick collection.

Introductory and more philosophical

http://www.sfu.ca/~swartz/pw/text/pw_all.pdf

Introductory not so philosophical/more formal

http://emilkirkegaard.dk/en/wp-content/uploads/0415400678.Routledge.Logic_.An_.Introduction.Dec_.2005.pdf

http://emilkirkegaard.dk/en/wp-content/uploads/0262511266.The_.MIT_.Press_.Logic_.Primer.-.2nd.Edition.Feb_.2001.pdf

http://emilkirkegaard.dk/en/wp-content/uploads/A-Concise-Introduction-To-Logic-Hurley-7th-ed.pdf

More advanced and very formal

http://emilkirkegaard.dk/en/wp-content/uploads/An-Introduction-to-Non-Classical-Logic-From-If-to-Is.pdf