# test inputs
A = [[1,2,3],
     [1,-1,0],
     [4,0,2],
     [1,1,1]]

B = [[-1,0,1,0],
     [6,3,0,3],
     [4,1,1,0]]

C = [[1,2,-3,1],
     [-5,1,0,-2],
     [1,-1,0,1]]


# returns matrix of 0's of given size
def zeros(nrow, ncol):
    R = [[0 for ???] for ???] # write your code instead of ???
    return R


# returns dimensions of matrix [nrow, ncol]
def size(M):
    s = [0, 0] # init vector of length 2
    s[0] = len(???) # write your code instead of ??? 
    s[1] = len(???) # write your code instead of ???
    return s


# check if two matrices can be added
def canMultiply(A,B):
    sizeA = size(A)
    sizeB = size(B)
    return ??? # write your code instead of ???

# check if two matrices can be multiplied
def canMultiply(A,B):
    sizeA = size(A)
    sizeB = size(B)
    return ??? # write your code instead of ???

# change rows and columns of A
def transpose(A):
    sizeA = size(A)
    # R is matrix of zeros in size of transposed A
    R = zeros(???) # write your code instead of ???
    # fill entries in R with values in A
    for i in range(???): # write your code instead of ???
        for j in range(???): # write your code instead of ???
            R[i][j] = ??? # write your code instead of ???
    return R

# omitt j-th column of A
def omittCol(A, j):
    sizeA = size(A)
    # init matrix of correct size 
    B = zeros(???, ???) # write your code instead of ???
    # for each row in A
    for i in range(???):
        a = ???
        del a[j]
        B[i] = ???
    return ???