An old tanur (that that has been heated the requisite amount to be susceptible to tumah; see 5:1)

inside of a new one (one that has not yet been heated the requisite amount and is therefore not susceptible to tumah; in this case the mouths of the two tanurs are at the same level)

and a mat is on the mouth of the old one (yet it is large enough to block the mouth of the new tanur as well, but it is not plastered in place, so there is no tight fitting seal on either oven)

if the old one is removed

and the mat will fall

everything is tamei [if they are under the same canopy as a cadaver]

and if not everything is tahor (if the new oven is holding up the mat, then it constitutes a separate canopy from that of the corpse, and so protects everything beneath it, including the old tanur).

[If the ovens were arranged with the one that was] new inside the old

and the mat was on the mouth of the old one,

if there is not between the new one and the mat

the space of a handbreadth (then we consider it as if it was resting atop the new one),

everything in the new one is tahor.

פרק י משנה ח

[Two or more] stewpots (which are made of earthenware),

one inside the other

and their rims are even,

if a sheretz is in the highest one (i.e. the innermost of these nested pots)

or the lowest one (the outermost),

it [the one holding the sheretz] is tamei

and all of [the rest of them] are tahor. 

If liquids could get in (because the pots had holes in them),

if the sheretz was in the top one

all of them are tamei,

[if the sheretz was] in the lower one it is tamei

and all [of the rest of] them are tahor;

If the sheretz was in the top one

and the lower one is higher,

it and the lower one is tamei.

[If the sheretz was] in the top one

and the lower one is higher

all [pots in between the top one and the lower one] that has sufficient liquid to moisten

is tamei.