High Quality Content by WIKIPEDIA articles! Property FA is a property of mathematical groups. Jean-Pierre Serre defined property FA in his book Arbres, amalgames, SL2 (published in English, translated by John Stilwell, as Trees). A group G is said to have property FA if every action of G on a tree has a global fixed point. Serre shows in Trees that if a group has property FA, then it cannot split as a free product with amalgamation or HNN extension. In particular, a finitely generated group with property FA has finite abelianization. It is a theorem of Watatani that Kazhdan's property (T) implies property FA of Serre.