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Description
Inverse SemigroupsSymmetry is one of the most important organising principles in the natural sciences. The mathematical theory of symmetry has long been associated with group theory, but it is a basic premise of this book that there are aspects of symmetry which are more faithfully represented by a generalization of groups called inverse semigroups. The theory of inverse semigroups is described from its origins in the foundations of differential geometry through to its
Symmetry is one of the most important organising principles in the natural sciences. The mathematical theory of symmetry has long been associated with group theory, but it is a basic premise of this book that there are aspects of symmetry which are more faithfully represented by a generalization of groups called inverse semigroups. The theory of inverse semigroups is described from its origins in the foundations of differential geometry through to its most recent applications in combinatorial group theory, and the theory tilings.
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4.2 ★★★★★
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Product Reviews
★★★★★ 5
Works way better than its price would suggest
Color: Storage Cover Black, Size: Rechargeable
A family member got frothed milk in their coffee and loved it, so they started doing it at home. They were using a wand mixer which is great at splashing milk all over creation but not very good at actually frothing it.
I asked them what kind of frother they wanted and they gave me 2 criteria: Rechargeable, and inexpensive. They didn't want to spend a lot on something they might not like or might outgrow, and they didn't want to constantly be looking for batteries.
This frother fits the bill. It recharges with a regular USB-C cable and comes with a short one (but not a wall plug so make sure you have one of those). It was also less than $11 delivered so not a lot to gamble on an occasional-use gadget.
Does it work? Absolutely, and a lot better than I ever thought it would. I was given a demonstration and in 10 seconds I saw a small cup of half and half turn into frothy foam. I'll admit, it does taste pretty good in coffee.
I 3D printed a stand to hold the mixer upright on the counter. Otherwise the base is too small and it tips over. That's not a complaint, just an observation. If you want it to stand upright, you'll have to do something similar. Otherwise, this thing is a good combination of simple, inexpensive, and effective.
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Reviewed in the United States on June 1, 2026
★★★★★ 5
Great Milk Frother for Coffee Lovers
Color: Storage Cover Black, Size: Rechargeable, Color: Storage Cover Black, Size: Rechargeable
I’m really happy with this electric milk frother. It is easy to use, rechargeable, and makes rich, creamy foam in just a few seconds. It works great for coffee, lattes, cappuccinos, and even hot chocolate. The design is sleek and comfortable to hold, and it is very easy to clean after use. The battery lasts well, and I like that I don’t need disposable batteries. Overall, this is a great product for anyone who enjoys making coffee drinks at home. Highly recommended!
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Reviewed in the United States on May 9, 2026
★★★★★ 5
Great purchase
Color: Storage Cover Black, Size: Rechargeable
I've had my Circle Joy Frother since May 11th, and I've have used it every day. It's the best frother I've ever ordered or owned. It's powerful, works great and it's rechargeable, no batteries to buy for this one. I'll buy this one again if or when it stops working. I'm very satisfied.
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Reviewed in the United States on May 28, 2026
★★★★★ 5
Game Changer for Coffee Lovers
Color: Storage Cover Black, Size: Rechargeable
I purchased the Circle Joy Rechargeable frother mostly because of the price. The frothy-whipped cream is a treat on the weekends, and the last hand frother I purchased zapped out. WoW - this one is amazing! The last one I had was battery operated, and wasn't as fast as this one. I now use it everyday because it works so quickly. It comes with a "lid" for the blender part, so I can toss in my briefcase. Love that recharges quickly so its ready when I am. Great price, easy to use, looks sleek, and tiny enough to take with you. LOVE, FiVE Stars
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Reviewed in the United States on May 26, 2026
★★★★★ 4
Great for short term
Color: Storage Cover Black, Size: Rechargeable
Works great when it works.... But I've bought three this year and two of them just unexpectedly died with no logical reason. Giving up and trying a new brand for my protein coffee drinks. *Edit....after original review the seller offered a refund and apologized for the issues I had. Bumping up my rating for proactive customer service and trying to make things right.
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Reviewed in the United States on May 23, 2026