<s>
In	O
mathematics	O
,	O
a	O
gradually	B-Algorithm
varied	I-Algorithm
surface	I-Algorithm
is	O
a	O
special	O
type	O
of	O
digital	B-Algorithm
surfaces	I-Algorithm
.	O
</s>
<s>
It	O
is	O
a	O
function	O
from	O
a	O
2D	O
digital	O
space	O
(	O
see	O
digital	B-Algorithm
geometry	I-Algorithm
)	O
to	O
an	O
ordered	O
set	O
or	O
a	O
chain	O
.	O
</s>
<s>
The	O
gradually	B-Algorithm
varied	I-Algorithm
surface	I-Algorithm
has	O
direct	O
relationship	O
to	O
graph	O
homomorphism	O
.	O
</s>
