I have seen definitions of regular polyhedra where it is assumed only that the faces are congruent and regular (equilateral). I have seen also definitions where two conditions are assumed:
- Congruent regular faces.
- Congruent Dihedral angles.
I belive that the condition (1) above implies the condition (2) above.
Is this right?
Update:
The following link: A congruence problem for polyhedra
Has the following :
Theorem 1.2 (Cauchy, 1839). Two convex polyhedra with corresponding congruent and similarly situated faces have equal corresponding dihedral angles.
I believe this is the line of search that I would go for.
Final Update: At this point the answers with counter-examples are good. I wanted to point out to the book in this link Polyhedra
A set of counter-examples is given in Figure 2.18. But most important is the following theorem:
Theorem: Let $P$ be a convex polyhedron whose faces are congruent regular polygons. Then the following statements about $P$ are equivalent:
- The vertices of $P$ all lie on a sphere.
- All the dihedral angles of $P$ are equal.
- All the vertex figures are regular polygons.
- All the solid angles are congruent.
- All the vertices are surrounded by the same number of faces.
Again, thanks to all who helped.
Perhaps the simplest counterexample is the bipyramid formed by sticking together two equal regular tetrahedra so that a face on each of them coincides.