definition
let D be non
empty set ;
let M be
Matrix of
D;
existence
ex b1 being Matrix of D st
( len b1 = width M & ( for i, j being Nat holds
( [i,j] in Indices b1 iff [j,i] in Indices M ) ) & ( for i, j being Nat st [j,i] in Indices M holds
b1 * (i,j) = M * (j,i) ) )
uniqueness
for b1, b2 being Matrix of D st len b1 = width M & ( for i, j being Nat holds
( [i,j] in Indices b1 iff [j,i] in Indices M ) ) & ( for i, j being Nat st [j,i] in Indices M holds
b1 * (i,j) = M * (j,i) ) & len b2 = width M & ( for i, j being Nat holds
( [i,j] in Indices b2 iff [j,i] in Indices M ) ) & ( for i, j being Nat st [j,i] in Indices M holds
b2 * (i,j) = M * (j,i) ) holds
b1 = b2
end;
theorem Th47:
for
x1,
x2,
y1,
y2 being
object holds
(
len ((x1,x2) ][ (y1,y2)) = 2 &
width ((x1,x2) ][ (y1,y2)) = 2 &
Indices ((x1,x2) ][ (y1,y2)) = [:(Seg 2),(Seg 2):] )
theorem Th48:
for
x1,
x2,
y1,
y2 being
object holds
(
[1,1] in Indices ((x1,x2) ][ (y1,y2)) &
[1,2] in Indices ((x1,x2) ][ (y1,y2)) &
[2,1] in Indices ((x1,x2) ][ (y1,y2)) &
[2,2] in Indices ((x1,x2) ][ (y1,y2)) )
theorem
for
D being non
empty set for
a,
b,
c,
d being
Element of
D holds
(
((a,b) ][ (c,d)) * (1,1)
= a &
((a,b) ][ (c,d)) * (1,2)
= b &
((a,b) ][ (c,d)) * (2,1)
= c &
((a,b) ][ (c,d)) * (2,2)
= d )
Lm1:
for D being non empty set
for M being Matrix of D
for k being Nat st k in dom M holds
M . k = Line (M,k)