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**Z**[1/2] or

**Q,**

**R**,

**C**), then the singular cohomology ring of a certain space G is the polynomial ring over [itex]\Lambda[/itex] in the Pontrjagin classes. But what is meant by a Pontrjagin class as an element of [itex]H^*(G,\Lambda)[/itex] ?? Is there a natural map [itex]H^*(G,\mathbb{Z})\rightarrow H^*(G,\Lambda)[/itex] that allows such an identification!?