How does Oracle use indexes?

A vendor has supplied an application with the following three indexes on a table:-

Index1 uses columns col1, col2, col3, col4, col5, col6.
Index2 uses columns col1, col2, col3.  
Index3 uses columns col1, col2.

I think index2 and index3 are redundant. The vendor says no.

Surely Oracle can use index1 in any situation when only some of those leading columns are needed! Can anyone shed light on this problem?

Thanks,

	Rick Williams
	The Flinders University of South Australia.