Table 1 The counts of different types of Delaunay tetrahedra in the test set of 5,757 PDB entries. Tetrahedron C_C_N_O_ (containing the peptide bound of amino acids) turns out to be the most frequent with 19, 463, 268 occurences in our test set. The frequency of other labels decrease exponentially.

C C N O

C C C O

C C C N

C C C C

C C O O

C N O O

C N N O

C C N N

C O O O

N N O O

N O O O

C C C S

C C O S

C N N N

C C N S

C N O S

O O O O

N N N O

C O O S

C C S S

C N N S

N O O S

C O S S

N N N N

C N S S

N N O S

O O O S

C C C SE

N O S S

C C O SE

C C N SE

C N O SE

N N N S

N N S S

C S S S

O O S S

N S S S

C O O SE

C N N SE

S S S S

O S S S

C C C F

N O O SE

C C F O

N N O SE

C O O P

C C F N

O O O P

C C SE SE

C F N O

N O O P

C C S SE

O O O SE

C C C I

C C I O

C F O O

C CL N O

C N O P

N N N SE

C I O O

C C CL N

C C CLO

C O S SE

AS C C S

AS C C O

C I N O

C N SE SE

AS C C C

C F N N

C C O P

AS C O S

C C C CL

F N O O

C O O V

C C I N

AS C N O

B C O O

C CLO O

AS C C N

C O SE SE

C C F S

O O O V

F N N O

C C I S

N N O P

AS C O O

AS N O O

C N S SE

B C N O

N N SE SE

B C C O

CL N O O

I O O O

I N O O

CL N N O

N O SE SE

F O O O

AS N N O

AS C N N

N O S SE

C I O S

C C F F

B N O O

C O P S

C F O S

AS C N S

O O S SE

C F F N

C C C P

O O P S

N N S SE

AS O O S

AS N O S

C CL N N